Diagnostic sensitivity of motor nerve conduction studies in ulnar neuropathy at the elbow.

Seventy-six patients with ulnar neuropathy at the elbow were divided into 3 classes (Grades I, II, and III) according to their clinical features and the maximal motor nerve conduction velocity (MCV), and the amplitude ratios at the across-elbow segment were retrospectively analyzed. To determine the criteria for abnormality, a control study was conducted on 150 healthy volunteers ranging in age from 20 to 89 years (6 age groups). The normal value for MCV could be set for two age groups: those under 60 and those over 60 years old. The 95% confidence limit was 54m/s for the former and 50m/s for the latter. There was no statistically significant difference in the amplitude ratio among the age groups. The confidence limit was set uniformly at 0.82 (above elbow/below elbow). An abnormality in either MCV or the amplitude ratio was found in 66.7% of Grade I (recent and mild symptoms), 89.7% of Grade II (persistent symptoms), and 100% of Grade III cases (marked intrinsic muscle atrophy). Evaluation using the combination of MCV and the amplitude ratio, considering the age-related normal value, appeared to be useful in establishing a differential diagnosis of ulnar neuropathy at the elbow.